Case sizing for .223 for AR-15
- Thread starter ZREXER
- Start date
mmcintyre1220
CGN frequent flyer
- Location
- Tillsonburg, Ontario
for any semi auto, ensure you are full length sizing with some over cam and always always trim your brass. IMO small base dies are absolutely unnecessary .
I always have a cam over on my press stroke. I do not trim every time though. I lock a caliper at max length and any that pass through get loaded and any that don't get trimmed. Haven't had an issue with my AR in over 800rnds since adopting this method.
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I use a small base die "once" with range pickup brass and when I buy bulk once fired brass. The small base die reduces the cases back to minimum dimensions after being fired in another chamber.
Any cases fired in my chamber are sized with a standard die. Most AR-15 chambers are slightly larger than a standard .223 chamber and a standard resizing die should work.
"BUT" nothing is written in stone and chambers and dies vary in size. Meaning if the resizing die does not reduce the case diameter enough and bump the shoulder back enough it can cause problems.
Not adjusting the die down far enough can cause problems, meaning 1/8 to 1/4 of a turn "more" after contact with the shell holder with press cam over. This amount varies depending on chamber and die dimensions.
Below measuring a "FIRED" case in my Hornady cartridge case headspace gauge. Then I adjust the die for .003 shoulder bump, and measuring this way before and after sizing ensures the case shoulder is shorter than the chamber.
Below case gauges vary in diameter, as you can see the reversed cases dropped further into the Wilson and Dillon case gauges. And the red J.P. Enterprise gauge is cut with a finish chamber reamer to minimum chamber dimensions and its diameter is smaller.
I drop all my resized cases and loaded ammunition into the J.P. Enterprise gauge. This check ensures the case body has been reduced enough in diameter. And also checks if the crimp is bulging around the case mouth. Some of you may think using two gauges might be overkill, but I'm loading for three AR15 and all ammunition chambers and ejects without any problem.
Bottom line, my guesses are either the case has not been sized enough or the case mouth is bulging from over crimping. And remember the case will spring back slightly after sizing. Meaning range pickup brass after being full length resized might still not fit in your chamber. And why I use a small base die on cases not fired in my rifle. And a small base die will reduce the case diameter more than a standard die and also push the shoulder back more.
And again, chambers and dies vary in size and a resizing die can over or under resize your cases. Example, I have a standard Lee .223 die that will size the cases smaller than my RCBS small base die.
Any cases fired in my chamber are sized with a standard die. Most AR-15 chambers are slightly larger than a standard .223 chamber and a standard resizing die should work.
"BUT" nothing is written in stone and chambers and dies vary in size. Meaning if the resizing die does not reduce the case diameter enough and bump the shoulder back enough it can cause problems.
Not adjusting the die down far enough can cause problems, meaning 1/8 to 1/4 of a turn "more" after contact with the shell holder with press cam over. This amount varies depending on chamber and die dimensions.
Below measuring a "FIRED" case in my Hornady cartridge case headspace gauge. Then I adjust the die for .003 shoulder bump, and measuring this way before and after sizing ensures the case shoulder is shorter than the chamber.
Below case gauges vary in diameter, as you can see the reversed cases dropped further into the Wilson and Dillon case gauges. And the red J.P. Enterprise gauge is cut with a finish chamber reamer to minimum chamber dimensions and its diameter is smaller.
I drop all my resized cases and loaded ammunition into the J.P. Enterprise gauge. This check ensures the case body has been reduced enough in diameter. And also checks if the crimp is bulging around the case mouth. Some of you may think using two gauges might be overkill, but I'm loading for three AR15 and all ammunition chambers and ejects without any problem.
Bottom line, my guesses are either the case has not been sized enough or the case mouth is bulging from over crimping. And remember the case will spring back slightly after sizing. Meaning range pickup brass after being full length resized might still not fit in your chamber. And why I use a small base die on cases not fired in my rifle. And a small base die will reduce the case diameter more than a standard die and also push the shoulder back more.
And again, chambers and dies vary in size and a resizing die can over or under resize your cases. Example, I have a standard Lee .223 die that will size the cases smaller than my RCBS small base die.
If you suspect a sizing problem and don't have a fancy case gauge, do the "plop" test for a quick and dirty test. Hold the upper muzzle down and drop your cartridge in the chamber, push it in a bit with your finger until fully seated. Reverse the upper to muzzle up and the cartridge should drop free. If it sticks in the chamber, it's not sized down enough and you may need a small base die.
- Location
- Hamilton, Ontario
I use a small base RCBS die and I fully size, then I trim all brass. I'm about 3 to 4k rounds and its been flawless
A picture is worth a thousand words, when full length resizing and squeezing the fired case it grows longer inside the die. And you must push the case shoulder back .003 to .006 shorter than the chamber. Meaning the case shoulder must be pushed back below the red dotted line in order to fit back in the chamber. And after resizing the cases they will spring back a little trying to get back to their fired size. The spring back amount depends on how hard the brass is, meaning the more the case is fired the harder the brass gets and springs back more.
Bottom line you must push the the case shoulder back far enough to compensate for brass spring back after sizing. And a few of your cases are a smidgen longer than your chamber and you need to force the bolt closed. So try adjusting the die down further to makeup for brass spring back. You can also try pausing at the top of the ram stroke for a few seconds, this reduces the amount of brass spring back and the case shoulder location will be more uniform.
Also you should trim the cases to the same length when crimping the bullet. And this is because a longer case can bulge just below the crimp making the case neck larger than the chamber.
I was starting to have similar problems and found it to be spring back with some Norc and some military brass, to counter this I size on my progressive with a lee sizing die in station one with a regular de-capping pin no expander then in station 3 I have an rcbs small base die with a Lyman carbide expander ball with the pin removed and have not had a single issue since setting up like this.
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If the die wasn’t screwed down and camming over, it wasn’t fully sizing the brass. Easy fix, and no additional dies, tools or drama really needed. They either fit the chamber or you’re going to be mortaring a few undersized rounds out of the chamber.
I’ve done the same whereby the die backed off on around 400 rounds that I had loaded up. My ARs barfed them up, but the Sig 550s chewed them up without so much as a hiccup.
I’ve done the same whereby the die backed off on around 400 rounds that I had loaded up. My ARs barfed them up, but the Sig 550s chewed them up without so much as a hiccup.
